This invention relates to gas meters and, in particular, four chamber gas meters in which the diaphragms are directly connected to the tangent by means of which the valve or valves which control the flow of gas from the inlet into the chambers and from the chambers to the outlet, are operated. Conventional four chamber meters are typified by the meters disclosed in U.S. Pat. Nos. 2,544,665 and 2,818,046. In such meters the control chamber, which contains the tangent and the control valves, is located vertically above the measuring chambers which contain the diaphragms and, of course, is pressure sealed from the measuring chambers. Because of this vertical orientation, the linkage between the diaphragms and the tangent is relatively complex. This complex linkage not only contributes to the cost of producing the meter, but also imposes an increased drive torque on the diaphragms and therefore an increased pressure drop across the meter which could be minimized if the diaphragms could be directly connected to the tangent. Direct drive meters in which the diaphragms are directly connected to the tangent or control crank have long been known in connection with three chamber meters such as shown in U.S. Pat. Nos. 373,003 to Bell, 2,005,024 to Diehl and 2,068,378 to Diehl. In such meters, the third or middle chamber is the chamber contained between the two diaphragms and is also the control chamber in which the control valve is located which controls the flow of gas from the control chamber to the diaphragms. However, a three chamber meter of a weight and physical size equivalent to a four chamber gas meter does not have as great a capacity as the four chamber meter in terms of cubic feet of gas which may be passed through the meter under the same conditions.
In order to directly connect the diaphragms to the tangent or the control crank which drives the control valve, it is generally necessary to locate the tangent or control crank between the diaphragms as shown in the aforementioned patents disclosing three chamber meters and as shown in the following U.S. patents which disclose direct connected four chamber meters: No. 16,049 to Darlington & Piper, No. 527,979 to Henley et al., No. 814,359 to Crawford, No. 889,652 to Armstrong and No. 1,676,651 to Huettig. It will be noted that in each case four chamber meters have four measuring chambers, two formed by each of the diaphragms, each of the measuring chambers being pressure sealed and discrete from each other and form the control chamber in which the control valves are located. Thus, in order to connect the diaphragms with the tangent or control crank, it is necessary that the linkage from at least one of the diaphragms sealingly penetrates a wall which separates the measuring chamber formed by that diaphragm from the other measuring chambers and the control chamber. The method by which this penetration is made from the measuring chambers into the control chamber is important in determining the amount of friction that the seal penetrating member imposes on the diaphragms which, of course, directly affects the efficiency of the meter and the pressure drop across the meter, both of which factors are extremely important in providing a commercially acceptable meter.
The patent to Darlington et al. shows a four chamber meter with the control linkage for the control valve located generally between the opposed diaphragm chambers; however, the diaphragms are not directly connected to the tangent or the control crank, and it will be noted that the rods I, by what means of which the motion of the diaphragms is transmitted to the control chamber and valve, require a reciprocating seal. In order to be effective, such seals impose a greater frictional load on the diaphragms than the seal for a rotary shaft would impose, thereby imposing an increased load on the diaphragms.
The patent to Henley et al. likewise shows a four chamber meter in which the control mechanism is located directly between the diaphragm chambers. However, in order to seal the in-board measuring chambers between the diaphragms and the diaphragm housings, which is necessary to provide a four chamber meter, the patentee found it necessary to provide supplementary sealing diaphragms I and J. Thus, the control shaft is not directly accessible for direct connection to the diaphragms and the added complication of the seal diaphragms I and J render this arrangement unnecessarily complex and expensive.
The patent to Crawford also shows a four chamber meter with the control mechanism and linkage oriented between the opposed measuring chambers. However, the arrangement disclosed is extremely complicated in that the motion of the diaphragms is transmitted out of the measuring chamber through a sealed rotating shaft 26, and this rotary motion is transmitted through links 31 and 32 to the control shaft. Thus, the connection between the diaphragms and the control shaft is indirect and extremely complicated and relatively expensive to produce.
The patent to Armstrong also shows a four chamber meter with the control linkage between the diaphragms and the control valve physically located between the opposed diaphragm chambers. Again, the arrangement disclosed is extremely complicated in that the motion of the diaphragms is first transmitted to cranks 20 through links 17, 18, 21 and 26, the rotation of the cranks 20 being converted to linear motion and transmitted to the control valves 27 by means of link 26.
The patent to Huettig similarly discloses a four chamber gas meter with a portion of the control linkage being oriented between the diaphragm chambers. However, again as in the case of the above-mentioned prior art, in order to transmit the motion of the diaphragm 5 to the control valves 12, it was necessary to employ an extremely complex drive linkage. Also, since no portion of the shaft 17 is directly accessible to the chamber 9, this arrangement does not disclose an arrangement in which the control shaft is accessible for direct connection to both diaphragms.
To solve the problems inherent in the prior art, applicant has developed a compact, economical arrangement in which the penetration into the control chamber 15 is by means of an easily sealed rotary shaft, the shaft having respective portions, of each of which are directly accessible in respective ones of the measuring chambers associated with the diaphragm compartments to produce a compact, economical and accurate gas meter employing a drive mechanism requiring a minimum of effort to operate the control mechanism as hereinafter more fully described.